Keckster
Well-Known Member
I recently signed up for HPAcademy and started working hard on their suspension tuning courses. With a lot of measuring and crunching numbers I feel like I have missed something since the stock springs from DF are almost double what I'm calculating. I've only calculated for the front so far as the numbers seem wildly off. Lets type it out for sanity and double check
Step 1) Determine desired suspension frequency
-Based on the following chart provided by HPAcademy I chose to use 1.5Hz as the target frequency. I have little experience on what frequency I'm looking for but based on the other options I believe this one makes the most sense as the goblin is definitely high performance street but not far enough to be considered a low down force car. If anyone has any insight of a frequency they would choose please let me know.
Step 2) Measure weight at front/rear
-My front build weight may not be fully accurate as I weighed it just before winter and made a few small changes but should be in the ball park.
-Front weight: 628.6 lbs.
-Corner weight: 628.6lbs/2 = 314.3 lbs.
Step 3) Measure Unsprung weight
-Front Unsprung weight: 89.5 lbs.
Step 4) Calculate Sprung weight
-At this point I also converted to SI units to stay consistent with the course calculations without have to convert constantly
-Front sprung weight: 314.3 lbs. - 89.5 lbs. = 236.7 lbs.
- 236.7 lbs. = 107.37 kg.
Step 4) Measure Motion ratio
Step 5) Spring rate(K) Math
Step 1) Determine desired suspension frequency
-Based on the following chart provided by HPAcademy I chose to use 1.5Hz as the target frequency. I have little experience on what frequency I'm looking for but based on the other options I believe this one makes the most sense as the goblin is definitely high performance street but not far enough to be considered a low down force car. If anyone has any insight of a frequency they would choose please let me know.
Step 2) Measure weight at front/rear
-My front build weight may not be fully accurate as I weighed it just before winter and made a few small changes but should be in the ball park.
-Front weight: 628.6 lbs.
-Corner weight: 628.6lbs/2 = 314.3 lbs.
Step 3) Measure Unsprung weight
-Front Unsprung weight: 89.5 lbs.
Step 4) Calculate Sprung weight
-At this point I also converted to SI units to stay consistent with the course calculations without have to convert constantly
-Front sprung weight: 314.3 lbs. - 89.5 lbs. = 236.7 lbs.
- 236.7 lbs. = 107.37 kg.
Step 4) Measure Motion ratio
-I did find a thread where Lonny posted that the front motion ratio is .65in. damper travel per 1in. suspension travel which would come out to a motion ratio of about 1.54
-When I did my own measurements I found a motion ratio of about 1.73
Step 5) Spring rate(K) Math
K wheel = M Sprung corner * 4π^2 * F^2
K wheel = 107.37 kg * 4π^2 * 1.5^2 = 9537.3 N/m * 1000 = 9.54 N/mm
K spring = K wheel * MR^2
K spring = 9.54 N/mm * 1.54^2 = 22.62 N/mm / .175 N/mm = 129.25 lbs./in. (Lonny MR)
K spring = 9.54 N/mm * 1.73^2 = 28.6 N/mm / .175 N/mm = 163.43 lbs./in. (measured MR)
Step 6) Purchase new springsBased on the calculations I found need somewhere between a 130 to 160 lbs./in. spring rate for the front end of the goblin. Obviously there are other driving factors than just the static weight but based on my studies into motorsports this appears to be a proper starting point. I see some seasoned goblin racers running upwards of 500 lbs in the front and lowering the rear spring rate to around 300 lbs. I would love to hear some reasoning into any calculated decisions in this department as I learn more.